This study is an unblinded, voluntary, open-label toxicity trial assessing zidovudine as a candidate for post-exposure chemoprophylaxis for health care workers sustaining occupational exposures to HIV. The 2 secondary purposes of this study are: 1) to assess the effect of zidovudine chemoprophylaxis on the temporal sequence of the appearance of markers of HIV infection should it occur in a HCW(s) taking zidovudine chemoprophylaxis; and 2) to describe the epidemiology of exposures to HIV for which zidovudine chemoprophylaxis is elected in institutions participating in this study. Zidovudine will be initiated as soon as possible, but no longer than 72 hours post exposure at a dose of 200mg 6 x per day for 3 days, followed by 200mg 5 x per day for 25 days; total treatment course is 28 days. Exposed health care workers will be followed for a minimum of 12 months, and for up to 60 months whenever possible. Individuals will be assessed for drug toxicity as well as for early signs of HIV infection.